Residual fuel oil may be defined as "the remaining heavy portion of crude oil after fractional distillation and cracking have taken place, with the viscosity of such residuum (which may be a blend) being higher than about 100 to 150 SSU (Saybolt Seconds Universal) at a temperature of 100.degree.F".
Conventional industrial distillate fuel oil burners, using forced atomizing air at ambient temperature, are not currently able to successfully burn residual fuel oil, even though such residual fuel oil, just prior to entering the burner, has been preheated to a temperature which results in a viscosity of 100 SSU of such residual fuel oil entering the burner.
It has been stated by many manufacturers of industrial forced atomizing ambient temperature air type fuel oil burners that their small capacity (maximum of approximately 10 gallons per hour) models of such type fuel oil burners will successfully burn only distillate oil, and that residual fuel oil, even though preheated to enter such small capacity oil burners at an oil viscosity of 100 to 150 SSU, cannot be successfully burned in small capacity burners.
Preheating residual oil to a higher temperature (than that required to reduce oil viscosity to 100 to 150 SSU) causes undesirable cracking and carbonization of the oil.
Furthermore, previous burner hot air constructions for burning residual oil usually cannot avoid initial unsuccessful combustion (when initial ignition of the residual fuel oil takes place) because of incomplete atomization and/or vaporization of the initial flow of residual fuel oil through the burner, until a heat exchanger inside or external to the burner has elevated the entering ambient temperature oil or forced atomizing and/or combustion air up to a burner internal heated air temperature adequate to elevate and/or maintain residual fuel oil flowing through the burner at a temperature at which the oil viscosity is reduced sufficiently to allow successful atomization by forced hot air pressure, with subsequent oil vaporization.
U.S. Pat. No. 2,219,917 (Oct. 29, 1940), hereby incorporated into this application by reference, describes a fuel oil burner for burning "heavy" (a residual) oil, by preheating part of the combustion air with gas by means of a Bunsen burner 25. The intended purpose of heated air is to heat such incoming heavy oil inside the burner, elevate oil temperature and reduce oil viscosity inside the burner, with such preheated air surrounding the burner oil flow tube 10 for the greater portion (but not the entire length) of the oil flow tube 10 inside the burner.
However, U.S. Pat. No. 2,219,917 cannot, to my best knowledge and belief, function as described. Its blower 16 supplies ambient temperature forced air (under positive pressure) exterior to the annular heating chamber 12 of the burner. Such ambient temperature forced air pressure in its air duct 13, supplied from blower 16, prevents flow of any preheated air from heating chamber 12 outward through annular orifices 27, inasmuch as there is no incoming air pressure which is higher than blower 16 air pressure. The forced ambient temperature air in air duct 13 will instead force air in duct 13 into heating chamber 12 through the annular orifices 27.
It is believed that this ambient temperature air, under pressure from blower 16, will instead exit from the burner at the location of Bunsen gas burner 25. Thus no heated air can ever enter the burner as described in such patent. Thus it is not believed that the preheating of the oil can be accomplished in the manner described in said patent.